Low-friction conveyor

ABSTRACT

A low-friction conveyor ( 10 ) including a conveyor belt ( 12 ) supported on self-contained rollers ( 32 ) riding along a carryway ( 22 ). The conveyor includes a modular conveyor belt constructed of a series of rows of belt modules ( 24, 25 ) connected into a loop by hinge joints between adjacent rows ( 26 ). The belt is supported on a carryway. Drive surfaces are accessible from the interior side ( 28 ) of the belt loop. Drive elements, such as sprockets ( 16 ), drive on the drive surfaces to move the belt along the carryway. The belt rollers are recessed inward of the outer side ( 29 ) of the belt loop and extend past the interior side of the belt loop. In this way, the rollers engage the carryway in low-friction, rolling contact.

BACKGROUND

This invention relates to power-driven conveyors and, more particularly,to low-friction conveyors using modular conveyor belts. The inventionalso relates to methods for making such conveyor belts.

When articles being conveyed on a moving conveyor start to back up,trailing articles push against leading articles. The result is a buildupof backline pressure, which is greatest on the lead articles. Too muchbackline pressure can crush or otherwise damage the articles and loadthe conveyor because of the dynamic friction between the moving conveyorand the stalled or slowly moving articles.

In the corrugated industry, stacks of corrugated sheets are conveyedalong a processing line. A common way to convey these stacks is withpowered roller conveyors. In these conveyors, parallel cylindricalrollers with axes of rotation transverse to the conveying direction arearranged to form a rolling conveyor bed. Drive belts are often used tocontact the rollers to rotate them and propel the stacks along theroller bed. To eliminate backline pressure by preventing consecutivestacks from bumping into each other, the roller conveyor is divided intosuccessive accumulation zones of fixed length The rollers in one zoneare powered independently of those in another zone. In this way, when adownstream stack is stopped in one zone of the conveyor, the trailingupstream stack can be moved from zone to zone and stopped in the zonejust upstream of the stopped downstream stack without contact. Variousdrive arrangements are used to achieve individual zonal control byselectively engaging the rollers in each zone with the drive belt.

In another version, a conveyor belt is flanked on each side by a rollerconveyor bed. The stack of corrugated sheets rests atop both rollerconveyor belts. Portions of the conveyor belt are raised and loweredinto and out of contact with the bottom of the stacks. When raised intocontact, the conveyor belt transports the stack along; when the belt islowered out of contact, the stack rests in place on the two rollerconveyor beds. Thus, each portion of the conveyor belt that can beraised and lowered defines an accumulation zone.

But these zero-back-pressure roller conveyors have shortcomings. Therollers have a tendency to freeze up or their mounting holes to wallowout over time, resulting in such performance deficiencies as increasedfriction against the conveyed stacks, a bumpy conveyor bed, andexcessive noise. Roller conveyors also cause a stack of corrugated toform an “elephant foot” as it is conveyed. There are a couple of causesfor the “elephant foot.” As the stack traverses the spacing betweenconsecutive rollers, the leading edge of the bottom-most sheets bumpsinto the upcoming roller. Each time this occurs, the sheets above tendto creep forward relative to the bottom sheets. Article creep is alsocaused by a wave effect. The weight of the stack on the bottom-mostsheets makes them conform to the rollers. The closer a sheet is to thebottom of the stack, the more it deforms around the rollers into theinter-roller gaps and adopts a wavy shape. As the stack moves over therollers, the wave dynamically propagates upward into the stack, causingadjacent sheets at the bottom of the stack to creep. On a long conveyingpath over many rollers, the side profile of the stack resembles an“elephant foot” with the leading edge of the bottom-most sheet laggingthe leading edge of the topmost sheets. If the “elephant foot” becomestoo exaggerated, the stack becomes unstable, and sheets tip over,requiring manual intervention to rearrange the stack.

One way to achieve zero back pressure and minimize the “elephant foot”problem is to use a series of conveyor belts, or chains, arranged end toend with a small space between consecutive belts. Each belt, which formsan accumulation zone, is individually controlled by its own drive trainand sprockets or pulleys. The flat conveying surfaces provided by thebelts avoid the bumpiness of a roller conveyor, and the “elephant foot”problem is minimized. But such an arrangement is more complex and costlyin that multiple sprockets, shafts, and drive motors are required tohandle all of the zones, especially in a long conveyor system.Furthermore, all these fixed-length zone systems cannot efficientlyaccumulate stacks of different sizes or stacks that take up moreconveyor space than the length of a zone or much less space then thelength of a zone.

Modular conveyor belts, especially modular plastic conveyor belts, arewidely used in the food processing industry to convey food and beverageproducts. These endless belts are generally looped around sets of drivesprockets or drums at opposite ends of a conveyor section. The productsare carried along the carryway portion of the belt's path, and the beltreturns below along a returnway. The belt is supported in the carryway,which can be a solid plate or wearstrips. The belt slides along thecarryway as it is driven. In most food-handling applications, thesebelts are relatively lightly loaded, and the friction between the beltand the carryway is not too great a problem

But, in transporting heavy loads, such as stacks of corrugated sheets,the friction between a belt and its carryway can be significant,requiring larger drive motors and resulting in accelerated belt wear andjerky belt motion. These are some of the reasons that roller conveyorsare usually used in the corrugated industry. And, in some applications,plant space is limited. Larger-diameter drive sprockets may not bepossible because of vertical space limitations on the spacing betweenthe belt's carryway and returnway. Big drive motors may also be unableto meet the space requirements. Furthermore, limitations on motor sizelimit conveyor length.

Thus, there is a need for a low-friction conveyor capable of compactlytransporting heavy loads and avoiding the problems caused by rollerconveyors.

SUMMARY

These needs and others are satisfied by a low-friction conveyor havingfeatures of the invention. The conveyor includes a modular conveyor beltconstructed of a series of rows of belt modules connected serially athinge joints to form an endless belt extending in width between oppositeedges. The belt, which is supported in a carryway, has a first sidefacing the carryway and an opposite second side. Drive surfaces on thebelt are accessible from the first side. A drive system includes driveelements that engage the drive surfaces to drive the belt along thecarryway in a direction of travel. The belt also includes rollers thatrotate about transverse axes parallel to the hinge joints. The rollersare recessed inward of the second side and extend past the first side ofthe belt to engage the carryway in low-friction rolling contact.

Another version of low-friction conveyor includes a carryway supportinga pair of modular conveyor belt loops in parallel. A drive system drivesthe pair of modular conveyor belt loops along the carryway in adirection of belt travel. Each of the modular conveyor belt loopsincludes a plurality of rollers extending from the interior of themodular conveyor belt loops to ride along the carryway in rollingcontact.

In a method for constructing a low-friction modular conveyor beltaccording to another aspect of the invention, a plurality of beltmodules, including roller-top belt modules, are interconnected in aseries of rows. The series of rows extends from a first row to a lastrow. An inside-out belt loop is formed with the rollers of the rollertop belts facing the interior of the belt loop. The first row is thenconnected to the last row to close the loop. A belt loop with rollers onthe interior of the loop is thereby formed.

DRAWINGS

These and other features and aspects of the invention, as well as itsadvantages, are described in more detail in the following description,appended claims, and accompanying drawings, in which:

FIG. 1 is an isometric view of a conveyor system embodying features ofthe invention;

FIGS. 2A, 2B, 2C, and 2D are top, side elevation, front elevation, andperspective views of a conveyor belt module usable in a conveyor systemas in FIG. 1;

FIG. 3 is an isometric view of a belt loop made of modules such as thatin FIG. 2;

FIG. 4 is a sectional view of the conveyor of FIG. 1 taken along line4-4 to illustrate the carryway support;

FIG. 5 is a similar view of another version of carryway usable with aconveyor as in FIG. 1; and

FIG. 6 is an isometric view of the conveyor system of FIG. 1 with theconveyor belts removed to show the drive system

DETAILED DESCRIPTION

A low-friction conveyor 10 embodying features of the invention is shownin FIG. 1. The conveyor includes a pair of side-by-side conveyor belts,such as modular conveyor belts 12, looped around rollers 14 at each end.The upper plane of the belts is supported on a carryway 22. The carrywayshown in this example is a plate carryway, but it could alternatively beformed by laterally spaced wearstrips parallel to the direction of belttravel 20. The carryway and the rollers are supported conventionally byframe structure in a conveyor frame (not shown in FIG. 1). The beltsreturn below the carryway in a returnway 23 supported by returnwayrollers 15. The belts are driven in parallel in the direction of belttravel by sprocket sets 16 mounted on drive shafts 17 located centrallyalong the returnway in the interior of the belt loop.

Each conveyor belt 12 is preferably a modular plastic conveyor belt,such as the Series 400 Roller Top Belt manufactured by Intralox, Inc. ofHarahan, La., USA. Each belt is preferably arranged in a bricklaypattern of two or more modules 24, 25 per row 26 to form a belt of anydesired width, but could just as well be molded to width with a singlemodule in each row. Each belt extends through its thickness from a firstside 28 to an opposite second side 29 and transversely in width betweenopposite edges 30, 31. Rollers 32 extend past the first side, but arerecessed inward of the second side. The rollers are arranged to rotateabout axes 34 transverse to the direction of belt travel. This is unlikethe regular construction of a roller top belt in which the rollers faceaway from the carryway to support articles conveyed along a carryway inrolling contact so as to provide low backline pressure to backed-uparticles. In this construction, however, each belt is built inside outso that the rollers instead ride along the carryway in low-frictioncontact. The second side 29 of the belt in this example forms agenerally flat conveying surface to support conveyed articles, such asstacks of corrugated sheets.

Further details of a roller-top conveyor belt module usable in theversion of FIG. 1 are shown in FIG. 2. The module 24 extends from afirst end 38 to a second end 39. Hinge elements 40 are spaced apartalong each end. Holes 42 are formed through the hinge elements toreceive a hinge pin 44 that connects serially adjacent modules togetherat a transverse hinge joint formed by the interleaved hinge elements ofthe interconnected modules. The hinge elements extend from transverseintermediate members 46 and are offset from one end to the other.Longitudinal intermediate members 48 connect between the transversemembers. Curved members 50, 51 between the transverse members formsupports for rollers 32. Roller axles 52 extend through bores 54 formedin the rollers. The axles are arranged on an axis 34 generally parallelto the hinge joints and the confined hinge pins. Drive surfaces 56,accessible from the first side 28 of the module, receive a driving forcefrom a drive element, such as a sprocket tooth. In this version, drivesurfaces 57 are also accessible from the second side 29 of the module.Thus, the module of FIG. 2 can be joined with other such modules, aswell as with other rollerless modules of otherwise similar constructionto make a conveyor belt 12 as in FIG. 1.

Two belt loops 60 made up of modules such as that in FIG. 2 are shown inFIG. 3. Each loop is constructed by first interconnecting series of rows26 of belt modules 24, 25 with hinge pins connecting adjacent rowstogether. Once a length of rows is formed, an inside-out loop is formedwith the rollers 32 facing the interior of the loop. The first and lastbelt rows 62, 63 at the ends of the length of belt are then joined by ahinge pin 44 through the interleaved hinge elements of the first andlast row. In this way, standard roller-top belt modules can be used toconstruct a low-friction belt merely by looping it inside out.

The contact of each belt 12 with the carryway 22 is shown in FIG. 4. Asshown, the belt and any conveyed load are supported by the rollers 32.The first surface of the belt 28 is spaced from the plate carryway bythe rollers. The plate is typically made of stainless steel and providesa smooth rolling surface for the rollers.

Another version of carryway is shown in FIG. 5. In this version, thecarryway is formed of wearstrips 23 running in the conveying directionand spaced apart across the width of the conveyor. The spacing isselected so that the wearstrips coincide with the positions of therollers 32 on the belt 12. The wearstrips can be supported on a plate oron individual supports 65, as shown in FIG. 5.

Details of an exemplary drive system 64 for the low-friction conveyor ofFIG. 1 are shown in FIG. 6. The drive system shown includes a drivemotor 66 whose shaft is coupled to a gear reducer 68. Drive shafts 17extend laterally from the gear reducer in opposite directions. Sprocketsets 16 are mounted on each drive shaft to drive each belt. The ends ofthe drive shafts opposite the gear reducer are rotatably supported inbearing blocks (not shown) in side channels 73 of a conveyor frame. Acentral support beam 75 is interrupted at the position of the drivesystem to allow the drive system components to fit compactly between thecarryway and the returnway. The side channels and the central supportbeam support the rollers 14, 15 and the carryway (not shown in FIG. 6).The individual sprockets 76, which serve as drive elements, have centralbores that admit the drive shaft. Teeth 78 on the periphery of eachsprocket engage the drive surfaces 57 of the belt 12 through the firstside 28, i.e., the interior side, of the belt loop. As the motor rotatesits shaft, the drive shaft, and the sprockets, each belt moves. Therollers on the inside of the belt act as wheels rolling along thecarryway and supporting the product load. The rolling friction betweenthis inverted roller-top belt and the carryway is much less than thesliding friction between a conventional belt and the carryway would befor equivalent product loads. Less power is required to drive thislow-friction system, which means that smaller drive components andlonger belts can be used. Smaller-diameter sprockets permit the carrywayand the returnway portions of the belt to be spaced more closely. Forexample, as shown in FIG. 1, the spacing D between the carryway and thelowest descent of the returnway is preferably no more than about a foot.Furthermore, a smaller motor means lower utility bills. It also meansthat the motor and the rest of the drive system can even be recessedinward of the opposite belt edges 30, 31 to save even more valuableplant space and avoid interference with processing stations and otherplant operations.

Although the invention has been described with respect to a preferredversion in compliance with the best mode requirement, other versions arepossible. For example, an inside-out roller-top belt withomnidirectional roller balls could alternatively be used to providelow-friction contact with the carryway. As another example, a singleinside-out roller-top belt driven conventionally by a sprocket drivesystem along the carryway would achieve the low-friction benefits of theinvention. Thus, the scope of the claims is not meant to be, and shouldnot be, limited to the description of the preferred version.

1. A low-friction conveyor comprising: a modular conveyor belt includinga series of rows of belt modules connected end to end at hinge jointsinto an endless belt having a width defined by opposite edges; acarryway supporting the modular conveyor belt; the modular conveyor beltfurther including: a first side facing the carryway and an oppositesecond side; and drive surfaces accessible from the first side of themodular conveyor belt; a drive system including drive elements drivinglyengaging the drive surfaces to drive the modular conveyor belt in adirection of travel along the carryway; the modular conveyor beltfurther including: a plurality of rollers rotatable about transverseaxes parallel to the hinge joints, the rollers recessed inward of thesecond side and extending past the first side of the modular conveyorbelt to engage the carryway in rolling contact.
 2. A low-frictionconveyor as in claim 1 comprising a pair of the modular conveyor beltsarranged parallel to each other.
 3. A low-friction conveyor as in claim1 comprising a returnway for the modular conveyor belt spaced along itsentirety within about one foot of the carryway.
 4. A low-frictionconveyor comprising: a carryway; a pair of modular conveyor belt loopssupported in parallel on the carryway; a drive system arranged to drivethe pair of modular conveyor belt loops along the carryway in adirection of belt travel; each of the modular conveyor belt loopsincluding a plurality of rollers extending from the interior of themodular conveyor belt loops to ride along the carryway in rollingcontact.
 5. A method for constructing a low-friction conveyor belt,comprising: interconnecting a plurality of belt modules, includingroller-top belt modules, into a series of belt rows extending from afirst row to a last row; forming an inside-out belt loop with therollers of the roller-top belt modules facing the interior of the loop;and connecting the first row to the last row to close the loop.